<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #div1{
            width: 200px;
            height: 200px;
            background: skyblue;
            position: absolute;
            right: 0;
        }
    </style>
</head>
<body style="height: 2000px;">
  <div id="div1"></div>
  <script>
      var timer = null;
      var oDiv = document.getElementById('div1');

      window.onscroll = function () {
          var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
          startMove(parseInt((document.documentElement.clientHeight-oDiv.offsetHeight)/2)+scrollTop)
      };
      function startMove(iTarget) {
          clearInterval(timer);
          timer = setInterval(function () {
              var speed = (iTarget-oDiv.offsetTop)/4;
              speed>0?Math.ceil(speed):Math.floor(speed);

              if(oDiv.offsetTop == iTarget){
                  clearInterval(timer);
              }
              else {
                  oDiv.style.top = oDiv.offsetTop+speed+'px';
              }

          },30)
      }


  </script>
</body>
</html>